Characterization of Surface Basicity

In contrast to acidity characterization with basic probes, the use of acidic molecules to probe surface basicity is far less satisfactory. In fact, all acidic (or electrophilic) molecules (Table 3.12) also contain accessible nucleophilic (basic) atoms. It seems impossible to find a molecule that actually only interacts specifically with basic sites. On the other hand, metal oxides that display significant surface basicity 

EF material free, alkali exchanged zeolites are used as quite mild basic catalysts. Light alkali and alkaline earth metal zeolites, such as Na-X, Na-Y [165], alkali-MOR, Na-A and Ca-A [166], have a mild Lewis acid behavior and do not appear to have strong basic character. The same occurs for Na-silica-alumina [167]. However, heavy alkali metal zeolites such as Cs-Y actually act as base catalysts, or rather as acid-base catalysts, for example for toluene side-chain alkylation. Stronger basic character arises from impregnation of alkali zeolites with alkali salts, later 

In the case of Ba-]3-alumina [172] and La-P-alumina, the surface apparently only exposes the large low valency cations, detectable by adsorbing bases, and very basic oxygen species that adsorb CO2 in the form of carbonates. The decomposition temperature of surface carbonates on Ba-P-alumina (BaAli20i9) has been followed by IR under outgassing, and compared with the same experiment using MgO. BaAli20i9 appears to be far more basic than pure alumina and most pure oxides but less basic than pure alkaline earth oxides. 

Perovskite-type phases can form when small cations and large cations combine in a mixed oxide. The surface, however, appears to be largely dominated by the large cations and basic oxide anions, as in the cases of BaTi03 [173], SrTi03 [171] and several lanthanum perovskites [174]. 

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